A stream editor reads the input stream consisting of the specified files (or standard input, if none are given), processes is line by line by applying a script consisting of edit commands, and writes resulting lines to standard output. The filename '-' may be used to read standard input.

The edit script is composed from arguments of -e options and script-files, in the given order. A single script argument may be specified as the first parameter.

with whitespace being permitted before or after addresses, and between the function character and the argument. The addresses and the address inverter (!) are used to restrict the application of a command to the selected line(s) of input.

Each command must be on a line of its own, except where noted in the synopses below.

The edit cycle performed on each input line consist of reading the line (without its trailing newline character) into the pattern space, applying the applicable commands of the edit script, writing the final contents of the pattern space and a newline to the standard output. A hold space is provided for saving the contents of the pattern space for later use.

A pattern address is a basic regular expression (see "BASIC REGULAR EXPRESSIONS"), between the delimiting character /. Any other character except \ or newline may be used to delimit a pattern address when the initial delimiter is prefixed with a backslash ('\').

If no address is given, the command selects every line.

If one address is given, it selects the line (or lines) matching the address.

Two addresses select a range that begins whenever the first address matches, and ends (including that line) when the second address matches. If the first (second) address is a matching pattern, the second address is not applied to the very same line to determine the end of the range. Likewise, if the second address is a matching pattern, the first address is not applied to the very same line to determine the begin of another range. If both addresses are line numbers, and the second line number is less than the first line number, then only the first line is selected.

The maximum permitted number of addresses is indicated with each function synopsis below.

The argument text consists of one or more lines following the command. Embedded newlines in text must be preceded with a backslash. Other backslashes in text are deleted and the following character is taken literally.

The line, or range of lines, selected by the address is deleted. The text (which must start on the line following the command) is written to standard output. With an address range, this occurs at the end of the range.

Print the contents of the pattern space: non-printable characters are shown in C-style escaped form; long lines are split and have a trailing ^'\' at the point of the split; the true end of a line is marked with a '$'. Escapes are: '\a', '\t', '\n', '\f', '\r', '\e' for BEL, HT, LF, FF, CR, ESC, respectively, and '\' followed by a three-digit octal number for all other non-printable characters.

Substitute the replacement string for the first substring in the pattern space that matches the regular expression. Any character other than backslash or newline can be used instead of a slash to delimit the regular expression and the replacement. To use the delimiter as a literal character within the regular expression and the replacement, precede the character by a backslash ('\').

Literal newlines may be embedded in the replacement string by preceding a newline with a backslash.

Within the replacement, an ampersand ('&') is replaced by the string matching the regular expression. The strings '\1' through '\9' are replaced by the corresponding subpattern (see "BASIC REGULAR EXPRESSIONS"). To get a literal '&' or '\' in the replacement text, precede it by a backslash.

Branch to the : function with the specified label if any s substitutions have been made since the most recent reading of an input line or execution of a t function. If no label is given, branch to the end of the script.

In the pattern space, replace all characters occurring in string1 by the character at the corresponding position in string2. It is possible to use any character (other than a backslash or newline) instead of a slash to delimit the strings. Within string1 and string2, a backslash followed by any character other than a newline is that literal character, and a backslash followed by an 'n' is replaced by a newline character.

These two commands begin and end a command list. The first command may be given on the same line as the opening { command. The commands within the list are jointly selected by the address(es) given on the { command (but may still have individual addresses).

The entire line is ignored (treated as a comment). If, however, the first two characters in the script are '#n', automatic printing of output is suppressed, as if the -n option were given on the command line.

The possible atoms of a BRE are: ., matching any single character; ^ and $, matching the null string at the beginning or end of a string, respectively; a bracket expressions, enclosed in [ and ] (see below); and any single character with no other significance (matching that character). A \ before one of: ., ^, $, [, *, \, matching the character after the backslash. A sequence of atoms enclosed in \( and \) becomes an atom and establishes the target for a backreference, consisting of the substring that actually matches the enclosed atoms. Finally, \ followed by one of the digits 0 through 9 is a backreference.

A ^ that is not first, or a $ that is not last does not have a special significance and need not be preceded by a backslash to become literal. The same is true for a ], that does not terminate a bracket expression.

The BRE bounds are: *, specifying 0 or more matches of the preceding atom; \{count\}, specifying that many repetitions; \{minimum,\}, giving a lower limit; and \{minimum,maximum\} finally defines a lower and upper bound.

A bracket expression is a list of characters, character ranges and character classes enclosed in [ and ] and matches any single character from the represented set of characters.

A character range is written as two characters separated by - and represents all characters (according to the character collating sequence) that are not less than the first and not greater than the second. (Ranges are very collating-sequence-dependent, and portable programs should avoid relying on them.)

enclosed in [: and :] and represents the set of characters as defined in ctype(3).

If the first character after [ is ^, the sense of matching is inverted.

To include a literal '^', place it anywhere else but first. To include a literal ']' place it first or immediately after an initial ^. To include a literal '-' make it the first (or second after ^) or last character, or the second endpoint of a range.

The special bracket expression constructs [[:<:]] and [[:>:]] match the null string at the beginning and end of a word respectively. (Note that neither is identical to Perl's '\b' atom.)

If this program is invoked with the name s2p it will act as a sed-to-Perl translator. After option processing (all other arguments are ignored), a Perl program is printed on standard output, which will process the input stream (as read from all arguments) in the way defined by the sed script and the option setting used for the translation.

The l command will show escape characters (ESC) as '\e', but a vertical tab (VT) in octal.

Trailing spaces are truncated from labels in :, t and b commands.

The meaning of an empty regular expression ('//'), as defined by sed, is "the last pattern used, at run time". This deviates from the Perl interpretation, which will re-use the "last last successfully executed regular expression". Since keeping track of pattern usage would create terribly cluttered code, and differences would only appear in obscure context (where other sed implementations appear to deviate, too), the Perl semantics was adopted. Note that common usage of this feature, such as in /abc/s//xyz/, will work as expected.

Collating elements (of bracket expressions in BREs) are not implemented.